In the past, there has been proposed a sheet post processing apparatus (Finisher) which sequentially receives the sheet subjected to printing processing discharged from an image forming apparatus and then carries out a binding processing. As a binding section carrying out a binding processing, there is a glue binding section. Every time a new sheet (sheet except the last one) is stacked in a processing tray, the glue binding section enables glue to be adhered to a specific position (a part corresponding to the binding margin) of the sheet at the uppermost position. Then, every time stacking a new sheet one by one on the sheet already discharged, a processing for adhering glue to the part corresponding to the binding margin is carried out.
The glue to be used by the glue binding section includes the liquid glue, the solid glue, the tape glue and the like. The glue waits in a state in which the adhering surface thereof is exposed so as to be capable of being adhered to a sheet quickly.
However, in a case in which the glue binding processing has not been carried out for a long time, the glue in the waiting state gets bad because the adhering surface thereof is dry, and the gluing strength is reduced. Thus, the gluing strength of the glue for bonding a first sheet and a second sheet is insufficient, and as a result, the first sheet may be peeled off.
Therefore, it is desired to bond the first sheet and the second sheet with sufficient gluing strength.